Drill bit



Aug. 13, 1963 R. D. ZIMMERMAN DRILL BIT Filed April 11, 1961 .0% S mm m m United States Patent 3,100,545 DRILL BIT Robert D. Zimmerman, Andover, N.J., assignor to Ingersoll-Rand Company, New York, N.Y., a corporation of New Jersey Filed Apr. 11, 1961, Ser. No. 102,164 6 (Zlaims. (til. 175-419) This invention relates to rock drill bits of the type adapted to cut rock by impact. More particularly the invention relates to detachable bits of that type secured to a drill steel by the firiction of tapered end of the drill rod in a tapered socket in the bit.

In designing a bit connection of this type the angle of taper is a compromise between a steep angle which will permit easy removal of the bit from the rod and a gradual taper which will provide tight frictional engagement. Also if the taper is slight the bursting efiect is objectionable. Further difficulty encountered is failure of the bit by ring off, that is the stresses set up in the socket cause separation of the socket from the head of the bit. When a tapered rod is introduced into a tapered bore its forward movement is arrested when the ring tension becomes sufiicient to overcome the longitudinal force. At this point the socket has increased in diameter. The socket itself is a blind hole being the extension of a solid head which carries the cutting edges. if the socket is to be considered as a number of longitudinal sections then each of these becomes a cantilever and, for a given amount of movement of the outer end of the socket, the stress next to the support becomes greater as the stress section along the support is increased. In the case of drill bits when this stress becomes too high there is failure by ring off, that is, the socket separates from the head of the bit.

It is an object of the invention to prevent such ring oil.

This is accomplished in a preferred embodiment by the tormation of an annular groove at the base of the socket of such dimension as to still leave the remaining section heavy enough to absorb compressive stresses during drilling and to permit suflicient flexibility to allow stretch in the socket wall necessary for gripping the tapered end of the drill steel.

Further objects and advantages of the construction and the nature of the invention will be more completely understood by reference to the following description taken in conjunction with the drawing which illustrate a preferred embodiment.

in the drawing,

FIGURE 1 is an end view of a detachable drill bit constructed in accordance with the practice of the invention, and

FIG. 2 is a longitudinal section of the drill bit taken along the line 2-2 and shows the bit mounted on the tapered end of the drill steel.

Referring to the drawing the bit comprises a body having a massive forward end 12 provided with cutting edges on suitable inserts '14 mounted in radial slots 16 cut in the sloping end faces '13 of the bit 10. Inserts 14 are brazed in place and are adapted rat the center to abut a ring 18 provided with a central hole 20 to permit passage of cleansing fluid introduced into the interior of the bit in through passage 11 in the drill steel 34 and conducted to the face of the bit by way of a central hole 22. Additional cleansing fluid passages 24 conduct such cleansing iiuid to the sloping end faces 13 of the bit between the inserts 14.. The rearward end of bit 10* shown at 26 is hollow being provided with a tapered bore 28 extending from the outer extremity at least part way into the rearward end 26 and forming a socket 30 into which "Ice the tapered end 32 of a drill steel 34 is adapted to be inserted. In this embodiment socket 30 has a cylindrical portion 36 extending from the tapered bore 28 almost to the bottom of socket 30. The bottom of socket 3i) terminates at a bottom past of minimum wall thickness thereby forming a stress distributing means which in this instance is produced by an undercut groove 38 at which the wall thickness of that socket becomes a minimum.

It is understood that bit 10 cuts by impact of the cutting edges of inserts 14 against the rock, such impact being transmitted from the drill steel 34, the tapered portion 32 of steel 34 and the taper 28 of socket 30 are designed so that there will be a slight stretch in the rearward portion 26 as the tapered end 32 is driven into the socket 30. This action results in increasing the contacting area of tapered end 32 with the walls of socket 30 for as the wall of the socket stretches the cylindrical part 36 comes into contact with the tapered end 32 of the drill steel. Inasmuch as the forward end '12 of the bit is rigid and of course does not stretch the juncture of the socket 30 with forward end 12 is subjected to high bending stresses and strains which tend to separate the rearward end 26 from the forward end 12. Inasmuch as the section of the wall of bit '10 is reduced at .gnoove 38, a certain flexibility is introduced which permits the stretching described without rupturing the metal. It is understood of course that the section of the bit Wall at groove 38 is sufiicient to carry the compressive torces produced by the drill impact. in this instance such strength is produced by making the outer wall of both the rear section 26 and the forward part 12 of a continuous taper trom the relatively thin wall at the extreme rear to the diameter at the cutting edges of inserts 14. For the purpose of suitable gripping action of the tapered ends 32 in socket 30, the taper has been found to be suitable at about 3 /2 with the axis of drill steel 34. This may be varied depending upon the size of the bit and the force of the blows transmitted.

Thus, by the above construction are accomplished, among others, the objects hereinbefore referred to.

I claim:

1. A detachable drill bit comprising a body with a forward end having cutting edges, a hollow rearward drill steel receiving socket of decreasing cross-sectional area in the direction of the cutting edges, for at least part of its length and stress distributing means disposed at the one end of said drill steel receiving socket for distributing the stress on said drill bit, said stress distributing means being an undercut groove.

2. A detachable drill bit comprising a body having a forward end provided with cutting edges and a hollow rearward drill steel receiving part, said hollow part being in form a blind socket for receiving a drill steel, and stress distributing means disposed at the lower end of said drill steel receiving part for distributing the stress on said receiving part when said drill steel is received in said drill receiving part, said stress distributing means being an undercut groove.

3. A detachable drill bit comprising a body having a forward end provided with cutting edges, a hollow rearward drill steel receiving socket, said socket being in form a blind socket, stress distributing means disposed at the lower end of said drill steel receiving socket for distributing the stress on said drill bit, said stress distributing means being an undercut groove thereby reducing the body wall cross-section.

4. A detachable drill bit comprising a body having a forward end provided with cutting edges and a hollow rearward drill steel receiving part, said hollow part being inform a blind socket tor receiving a drill steel and being provided with a body wall which is cylindrical for part of its depth, stress distributing means in said blind socket comprising an undercut groove, said body wall converging inwardly :for part of its depth.

5. A detachable drill bit comprising a body having a 5 forward. end provided with cutting edges and a hollow rearward drill steel receiving part, said hollow part being in form a blind socket for receiving a drill steel and being provided with a body Wall which has a cylindrical portion for part of its depth, and stress distributing means 10 in said blind socketcomprising an undercut groove reducing the thickness of said body wall, said body wall converging inwardly for part of its depth and said cylindrical portion being disposed intermediate the converging part and said groove.

6. A detach-able drill bit comprising a body having a forward end provided with cutting edges and a hollow rearward drill steel receiving part, said hollow part being in form a blind socket :for receiving a drill steel and being provided with a body wall which has a cylindrical portion for part of its depth, and stress distributing means in said b-l-ind socket comprising an undercut groove reducing the thickness of said body Wall, said body wall converging inwardly for part of its depth and said cylindrical portion being disposed intermediate the converging part and said groove, said body having an outer wall tapering to a maximum diameter at said cutting edges.

Liddicoat Mar. 4, 1941 Sandvig June 9, 1959 

1. A DETACHABLE DRILL BIT COMPRISING A BODY WITH A FORWARD END HAVING CUTTING EDGES, A HOLLOW REARWARD DRILL STEEL RECEIVING SOCKET OF DECREASING CROSS-SECTIONAL AREA IN THE DIRECTION OF THE CUTTING EDGES, FOR AT LEAST PART OF ITS LENGTH AND STRESS DISTRIBUTING MEANS DISPOSED AT THE ONE END OF SAID DRILL STEEL RECEIVING SOCKET FOR DISTRIBUTING THE STRESS ON SAID DRILL BIT, SAID STRESS DISTRIBUTING MEANS BEING AN UNDERCUT GROOVE. 